Utilizing Soil Nails: Unique Temporary Shoring Project

In early 2016, URETEK MA was contacted to assist in the installation of the shoring for a Wet Well Cofferdam, at a Wastewater Pump Station in South Carolina. UMA was contacted to serve as a Design-Build subcontractor, on a temporary shoring project that had run into unforeseen conditions. The original plan was to drive in a ring of sheeting, supported internally by concrete walers. The PZ-27 sheets were driven to refusal, ranging in depth from 20-30 feet below grade. Due to unforeseen conditions, boulders were encountered at varying depths. The sheets were not able to be driven to full depth, because of these bouldery conditions, and the sheet pile driving operation had to be suspended.

The general contractor contacted the designer of the sheet pile system, who fabricated a solider pile design, to be placed inside of the previously installed sheeting. UMA value engineered the solider pile wall design, by utilizing a drilled and grouted soil nail wall with a flexible facing, within the sheet pile wall. This design included walers for the top two rows of soil nails, so that they could be tensioned and locked off, against the outside face of the existing sheet piles. UMA utilized the walers where the soil nail wall encountered the sheet piles, to help distribute the load evenly across the uneven sheet pile facing. The post-tension process utilized a hydraulic jacking system, to insure the sheeting and the soil nail system, were placed in an “active environment.”

Throughout the project, UMA coordinated closely with the general contractor to install the soil nail wall system. As the excavation moved deeper into the ground, the boulders the sheet piles were encountering, needed to be removed. The work site, due to its proximity to a neighborhood, was a no blast zone, and the general contractor worked to remove the large boulders via hydraulic hammers, and Dexpan. UMA installed the flexible facing soil nail wall, and successfully continued the excavation to full depth- totaling at 43-feet from top of excavation, to bottom of excavation. The excavated area totaled 50-feet in diameter, and required all equipment to be craned in, and out of, the work area daily.

This unique work site, coupled with the unforeseen issues with the boulders, allowed UMA the opportunity to offer a fresh perspective, and cost-effective solution. The soil nail wall combined with the walers, allowed the necessary excavations to be completed, and the Wet Well Cofferdam to be placed on schedule.